Catalogs: Resource Description and Discovery

Information retrieval techniques span a spectrum from full-text search, which
is a high-recall technique which makes little demand on the information
representation, to knowledge-base query, which is a high-precision technique,
which depends on a rich information representation.

Catalogs are databases structured for the purpose of browsing, searching,
and generally organizing large volumes of related data, or more often:
metadata. see also: design issues, where TimBL is writing about metadata again. 97-02-07 connolly

Metadata has two main functions:

to provide a means to discover that the data set exists and how it might
be obtained or accessed; and

to document the content, quality, and features of a data set and so give
an indication of its fitness for use.

A catalog records is generally not a primary resource, but rather a surrogate,
excerpt, abstract, or description giving some attributes of another resource.
The question arises: whence comes the list of attributes? What's the expressive
capability, structure, and meaning of attribute values?

A PICS label represents a set of
category/value pairs, where the categories are part
of a globally unique rating system. (While PICS 1.1 allows only
for floating point values, an enhancement to accomodate string values is
expected.)

PICS categories can serve as metadata attributes. Their meaning is given
in the rating system. The structure of a PICS label is similar to:

a row in a relational database table (a rating system is analagous to the
schema),

set of header names and values in an email message (the rating system is
RFC822),

Research Notes

Comment: So you will have to encode binary data? This is
expensive.
Response: Focus on the object-model. Is it complete? Consistent?
Web Collections are just a convenient vehicle for
expressing the object model; if there is a better way
of expressing the model, we'll use it.
Question: Who manages the link "types" (e.g., registration)?
Answer: Core link types ("core" to implementing WEBDAV) are
defined in the specification. Other "types" owned and
managed various groups (e.g., Dublin Core). Namespace
convention for link types is schema.(schema.type).
Response: Take care! Define namespace requirements for links so
that WEBDAV complies with the "Schema" work group
(Chris Weider, Chair).
Comment: Why be non-extensible w.r.t. the link definition? Allow
other fields to be added to the core fields (source,
dest, type).
Comment: PICS is doing meta-data. The authors would be well
advised to look at the PICS effort.